In times of the Exodus was Sol considered as single isolated star system which isn't directly connected with other systems in the Milky Way Galaxy. Humans from Western Alliance which escaped to the Sirius sector needed dealt first with many obstacles, learn about the Nomads threat ... and then find a way how to defeat them, like happened in the Dyson Sphere and later in the X-3043 crossroad. It was exactly the liberation of the X crossroad system which led to reveal of the Nephele system where was found wreck of abandoned Eastern Coalition sleepership "Stalin".
Data found in sleepership navigation computer has led first to Dublin and then to Hyperion where was found warp anomaly which was a long lost way back to the human's cradle. Also now was Sol seen as "sector with just one system", but there was now available functional inter-sector connection. Chain of events some time later led to reveal of another inter-sector connection to the Altair sector and answered what exactly happened with the "old" Eastern Coalition. In the meantime, when was Earth in "rebuild" state, was started intensive exploration of local space. There it was it, when was found that Sol is not just one single system in this Milky Way sector.
Note: first reveal of the jumphole located in the Sol system is described here: Crossfire Short Stories Part XVII: New discoveries in the Sol system?